Review on intermediate filaments of the nervous system and their pathological alterations

Acute-Phase Neurofilament Light and Glial Fibrillary Acidic Proteins in Cerebrospinal Fluid Predict Long-Term Outcome After Severe Traumatic Brain Injury

BACKGROUND

This study investigated trajectory profiles and the association of concentrations of the biomarkers neurofilament light (NfL) and glial fibrillary acidic protein (GFAP) in ventricular cerebrospinal fluid (CSF) with clinical outcome at 1 year and 10-15 years after a severe traumatic brain injury (sTBI).

METHODS

This study included patients with sTBI at the Neurointensive Care Unit at Sahlgrenska University Hospital, Gothenburg, Sweden. The injury was regarded as severe if patients had a Glasgow Coma Scale ≤ 8 corresponding to Reaction Level Scale ≥ 4. CSF was collected from a ventricular catheter during a 2-week period. Concentrations of NfL and GFAP in CSF were analyzed with enzyme-linked immunosorbent assay. The Glasgow Outcome Scale (GOS) was used to assess the 1-year and 10-15-year outcomes. After adjustment for age and previous neurological diseases, logistic regression was performed for the outcomes GOS 1 (dead) or GOS 2-5 (alive) and GOS 1-3 (poor) or GOS 4-5 (good) versus the independent continuous variables (NfL and GFAP).

RESULTS

Fifty-three patients with sTBI were investigated; forty-seven adults are presented in the article, and six children (aged 7-18 years) are described in Supplement 1. The CSF concentrations of NfL gradually increased over 2 weeks post trauma, whereas GFAP concentrations peaked on days 3-4. Increasing NfL and GFAP CSF concentrations increased the odds of GOS 1-3 outcome 1 year after trauma (odds ratio [OR] 1.73, 95% confidence interval [CI] 1.07-2.80, p = 0.025; and OR 1.61, 95% CI 1.09-2.37, p = 0.016, respectively). Similarly, increasing CSF concentrations of NfL and GFAP increased the odds for GOS 1-3 outcome 10-15 years after trauma (OR 2.04, 95% CI 1.05-3.96, p = 0.035; and OR 1.60, 95% CI 1.02-2.00, p = 0.040).

CONCLUSIONS

This study shows that initial high concentrations of NfL and GFAP in CSF are both associated with higher odds for GOS 1-3 outcome 1 year and 10-15 years after an sTBI, implicating its potential usage as a prognostic marker in the future.

Unique Role of Vimentin in the Intermediate Filament Proteins Family

Intermediate filaments (IFs), being traditionally the least studied component of the cytoskeleton, have begun to receive more attention in recent years. IFs are found in different cell types and are specific to them. Accumulated data have shifted the paradigm about the role of IFs as structures that merely provide mechanical strength to the cell. In addition to this role, IFs have been shown to participate in maintaining cell shape and strengthening cell adhesion. The data have also been obtained that point out to the role of IFs in a number of other biological processes, including organization of microtubules and microfilaments, regulation of nuclear structure and activity, cell cycle control, and regulation of signal transduction pathways. They are also actively involved in the regulation of several aspects of intracellular transport. Among the intermediate filament proteins, vimentin is of particular interest for researchers. Vimentin has been shown to be associated with a range of diseases, including cancer, cataracts, Crohn's disease, rheumatoid arthritis, and HIV. In this review, we focus almost exclusively on vimentin and the currently known functions of vimentin intermediate filaments (VIFs). This is due to the structural features of vimentin, biological functions of its domains, and its involvement in the regulation of a wide range of basic cellular functions, and its role in the development of human diseases. Particular attention in the review will be paid to comparing the role of VIFs with the role of intermediate filaments consisting of other proteins in cell physiology.

Serum neurofilament light chain levels are associated with all-cause mortality in the general US population

INTRODUCTION

Serum neurofilament light chain (sNfL) levels are biomarkers of neuro-axonal injury in multiple neurological diseases. Little is known on their potential role as prognostic markers in people without known neurological conditions.

OBJECTIVE

The aim of this study is to evaluate the association between sNfL levels and all-cause mortality in a general population setting.

METHODS

sNfL levels were measured in 2071 people aged 25-75 years from the general US population that participated in the 2013-2014 cycles of the National Health and Nutrition Examination Survey (NHANES). Cognitive function was evaluated in a subset of participants aged 60-75 years using the Consortium to Establish a Registry for Alzheimer's Disease-Word Learning test, the Animal Fluency test and the Digit Symbol Substitution test. We applied Cox proportional hazard models adjusted for several potential confounders to evaluate the association between sNfL and all-cause mortality through December 2019 by linking NHANES data with data from the National Death Index.

RESULTS

In a cross-sectional analysis, higher sNfL levels were associated with worse performance in all three cognitive function tests. Over a median follow-up of 6.1 years, 85 participants died. In a multivariable model adjusted for age, sex, race-ethnicity, diabetes, chronic kidney disease, harmful alcohol consumption, cigarette smoke and prevalent cardiovascular disease, higher sNfL levels were significantly and positively associated with all-cause mortality (HR per unit increase in log-transformed sNfL: 2.46, 95% CI 1.77-3.43, p < 0.001). Results were robust when analyses were stratified according to age, sex, body mass index and kidney function.

CONCLUSION

We found a positive association between sNfL levels and mortality in the general US population. Further studies are needed to understand the biological mechanisms underlying this association.

Diabetes Mellitus is Associated With Higher Serum Neurofilament Light Chain Levels in the General US Population

CONTEXT

Serum neurofilament light chain (sNfL) levels are biomarkers of neuroaxonal injury in multiple neurological diseases.

OBJECTIVE

Given the paucity of data on the distribution of sNfL levels in the general population, in the present study we identified predictors of sNfL levels in a community setting and investigated the association between diabetes and sNfL.

METHODS

sNfL levels were measured in 2070 people aged 20 to 75 years from the general US population (275 with and 1795 without diabetes) that participated in the 2013-2014 cycle of the National Health and Nutrition Examination Survey. We evaluated the association between diabetes and sNfL levels after adjustment for age, sex, race-ethnicity, alcohol use, and kidney function using a multivariable linear regression model. Cognitive function was evaluated in a subset of participants aged 60 to 75 years using the Consortium to Establish a Registry for Alzheimer's Disease-Word Learning test, the Animal Fluency test, and the Digit Symbol Substitution test.

RESULTS

The weighted prevalence of diabetes was 10.4% (95% CI, 9.0-11.9). In each age stratum, patients with diabetes exhibited higher sNfL levels compared with nondiabetic participants. Age, proportion of males, prevalence of diabetes, and homeostatic model of insulin resistance increased progressively across quartiles of sNfL levels in the overall population, whereas estimated glomerular filtration rate (eGFR) showed an opposite trend. In the multivariable model, age, sex, eGFR, alcohol use and diabetes were significantly associated with sNfL levels. Moreover, higher sNfL levels were associated with worse performance in all 3 cognitive function tests.

CONCLUSION

Diabetes is associated with higher sNfL. Further large-scale and prospective studies are needed to replicate our results and evaluate the ability of sNfL to predict the incidence of neuropathy and dementia in this patient population.

Neurofilaments in neurologic disorders and beyond

Many neurologic diseases can initially present as a diagnostic challenge and even when a diagnosis is made, monitoring of disease activity, progression and response to therapy may be limited with existing clinical and paraclinical assessments. As such, the identification of disease specific biomarkers provides a promising avenue by which diseases can be effectively diagnosed, monitored and used as a prognostic indicator for long-term outcomes. Neurofilaments are an integral component of the neuronal cytoskeleton, where assessment of neurofilaments in the blood, cerebrospinal fluid (CSF) and diseased tissue has been shown to have value in providing diagnostic clarity, monitoring disease activity, tracking progression and treatment efficacy, as well as lending prognostic insight into long-term outcomes. As such, this review attempts to provide a glimpse into the structure and function of neurofilaments, their role in various neurologic and non-neurologic disorders, including uncommon conditions with recent knowledge of neurofilament-related pathology, as well as their applicability in future clinical practice.

Evaluation of serum neurofilament light in the early management of mTBI patients

OBJECTIVES

Serum S100B allows a one-third reduction of computed tomography (CT) scans performed for mild traumatic brain injury (mTBI) patients. In this study, we evaluated the diagnostic performance of serum NF-L in the detection of intracranial lesions induced by mTBI.

METHODS

One hundred seventy-nine adult mTBI patients presenting to the emergency department of Clermont-Ferrand University Hospital with a Glasgow Coma Scale (GCS) score of 14-15 were included. S100B assays were performed for clinical routine while NF-L samples were stored at -80 °C until analysis. CT scans were performed for patients with S100B levels above the decision threshold of 0.10 μg/L. Later, NF-L and S100B levels were compared to CT scan findings to evaluate the biomarkers' performances.

RESULTS

The area under the ROC curve (AUC) evaluating the diagnostic ability in the prediction of intracranial lesions was 0.72 (95% CI; 0.58-0.87) for S100B and 0.58 (95% CI; 0.45-0.71) for NF-L, the specificities (at a threshold allowing a 100% sensitivity) were 35.7% for S100B, and 28% for NF-L (p=0.096). AUCs of NF-L and S100B for the identification of patients with neurological disorders were statistically different (p<0.001). The AUCs were 0.87 (95% CI; 0.82-0.93) for NF-L and 0.57 (95% CI; 0.48-0.66) for S100B. There was a poor correlation between NF-L and S100B, and NF-L levels were correlated to patients' age (Spearman coefficient of 0.79).

CONCLUSIONS

NF-L showed poor performances in the early management of mTBI patients. NF-L levels are strongly correlated to neurodegeneration, whether physiological, age-related, or pathological.

Neurofilament light chain and glial fibrillary acidic protein levels in metachromatic leukodystrophy

Metachromatic leukodystrophy is a lethal metabolic leukodystrophy, with emerging treatments for early disease stages. Biomarkers to measure disease activity are required for clinical assessment and treatment follow-up.

This retrospective study compared neurofilament light chain and glial fibrillary acidic protein (GFAP) levels in CSF (n = 11) and blood (n = 92) samples of 40 patients with metachromatic leukodystrophy (aged 0–42 years) with 38 neurologically healthy children (aged 0–17 years) and 38 healthy adults (aged 18–45 years), and analysed the associations between these levels with clinical phenotype and disease evolution in untreated and transplanted patients. Metachromatic leukodystrophy subtype was determined based on the (expected) age of symptom onset. Disease activity was assessed by measuring gross motor function deterioration and brain MRI. Longitudinal analyses with measurements up to 23 years after diagnosis were performed using linear mixed models.

CSF and blood neurofilament light chain and GFAP levels in paediatric controls were negatively associated with age (all P < 0.001). Blood neurofilament light chain level at diagnosis (median, interquartile range; picograms per millilitre) was significantly increased in both presymptomatic (14.7, 10.6–56.7) and symptomatic patients (136, 40.8–445) compared to controls (5.6, 4.5–7.1), and highest among patients with late-infantile (456, 201–854) or early-juvenile metachromatic leukodystrophy (291.0, 104–445) and those ineligible for treatment based on best practice (291, 57.4–472). GFAP level (median, interquartile range; picogram per millilitre) was only increased in symptomatic patients (591, 224–1150) compared to controls (119, 78.2–338) and not significantly associated with treatment eligibility (P = 0.093). Higher blood neurofilament light chain and GFAP levels at diagnosis were associated with rapid disease progression in late-infantile (P = 0.006 and P = 0.051, respectively) and early-juvenile patients (P = 0.048 and P = 0.039, respectively). Finally, blood neurofilament light chain and GFAP levels decreased during follow-up in untreated and transplanted patients but remained elevated compared with controls. Only neurofilament light chain levels were associated with MRI deterioration (P < 0.001).

This study indicates that both proteins may be considered as non-invasive biomarkers for clinical phenotype and disease stage at clinical assessment, and that neurofilament light chain might enable neurologists to make better informed treatment decisions. In addition, neurofilament light chain holds promise assessing treatment response. Importantly, both biomarkers require paediatric reference values, given that their levels first decrease before increasing with advancing age.

Cytoskeletal proteins as glioblastoma biomarkers and targets for therapy: A systematic review

Glioblastoma, the most common primary brain malignancy, is an exceptionally fatal cancer. Lack of suitable biomarkers and efficient treatment largely contribute to the therapy failure. Cytoskeletal proteins are crucial proteins in glioblastoma pathogenesis and can potentially serve as biomarkers and therapeutic targets. Among them, GFAP, has gained most attention as potential diagnostic biomarker, while vimentin and microtubules are considered as prospective therapeutic targets. Microtubules represent one of the best anti-cancer targets due to their critical role in cell proliferation. Despite testing in clinical trials, the efficiency of taxanes, epothilones, vinca-domain binding drugs, colchicine-domain binding drugs and γ-tubulin binding drugs remains to be confirmed. Moreover, tumor treating field that disrupts microtubules draw attention because of its high efficiency and is called "the fourth cancer treatment modality". Thereby, because of the involvement of cytoskeleton in key physiological and pathological processes, its therapeutic potential in glioblastoma is currently extensively investigated.

Astrocyte responses to nanomaterials: Functional changes, pathological changes and potential applications

Astrocytes are responsible for regulating and optimizing the functional environment of neurons in the brain and can reduce the adverse impacts of external factors by protecting neurons. However, excessive astrocyte activation upon stimulation may alter their initial protective effect and actually lead to aggravation of injury. Similar to the dual effects of astrocytes in the response to injury within the central nervous system (CNS), nanomaterials (NMs) can have either toxic or beneficial effects on astrocytes, serving to promote injury or inhibit tumors. As the important physiological functions of astrocytes have been gradually revealed, the effects of NMs on astrocytes and the underlying mechanisms have become a new frontier in nanomedicine and neuroscience. This review summarizes the in vitro and in vivo findings regarding the effects of various NMs on astrocytes, focusing on functional alterations and pathological processes in astrocytes, as well as the possible underlying mechanisms. We also emphasize the importance of co-culture models in studying the interaction between NMs and cells of the CNS. Finally, we discuss NMs that have shown promise for application in astrocyte-related diseases and propose some challenges and suggestions for further investigations, with the aim of providing guidance for the widespread application of NMs in the CNS.

From biomechanics to pathology: predicting axonal injury from patterns of strain after traumatic brain injury

The relationship between biomechanical forces and neuropathology is key to understanding traumatic brain injury. White matter tracts are damaged by high shear forces during impact, resulting in axonal injury, a key determinant of long-term clinical outcomes. However, the relationship between biomechanical forces and patterns of white matter injuries, associated with persistent diffusion MRI abnormalities, is poorly understood. This limits the ability to predict the severity of head injuries and the design of appropriate protection. Our previously developed human finite element model of head injury predicted the location of post-traumatic neurodegeneration. A similar rat model now allows us to experimentally test whether strain patterns calculated by the model predicts in vivo MRI and histology changes. Using a controlled cortical impact, mild and moderate injuries (1 and 2 mm) were performed. Focal and axonal injuries were quantified with volumetric and diffusion 9.4 T MRI at 2 weeks post injury. Detailed analysis of the corpus callosum was conducted using multi-shell diffusion MRI and histopathology. Microglia and astrocyte density, including process parameters, along with white matter structural integrity and neurofilament expression were determined by quantitative immunohistochemistry. Linear mixed effects regression analyses for strain and strain rate with the employed outcome measures were used to ascertain how well immediate biomechanics could explain MRI and histology changes. The spatial pattern of mechanical strain and strain rate in the injured cortex shows good agreement with the probability maps of focal lesions derived from volumetric MRI. Diffusion metrics showed abnormalities in the corpus callosum, indicating white matter changes in the segments subjected to high strain, as predicted by the model. The same segments also exhibited a severity-dependent increase in glia cell density, white matter thinning and reduced neurofilament expression. Linear mixed effects regression analyses showed that mechanical strain and strain rate were significant predictors of in vivo MRI and histology changes. Specifically, strain and strain rate respectively explained 33% and 28% of the reduction in fractional anisotropy, 51% and 29% of the change in neurofilament expression and 51% and 30% of microglia density changes. The work provides evidence that strain and strain rate in the first milliseconds after injury are important factors in determining patterns of glial and axonal injury and serve as experimental validators of our computational model of traumatic brain injury. Our results provide support for the use of this model in understanding the relationship of biomechanics and neuropathology and can guide the development of head protection systems, such as airbags and helmets.

Pharmacological blockers of CCR5 and CXCR4 improve recovery after traumatic brain injury

CCR5 and CXCR4 are structurally related chemokine receptors that belong to the superfamily of G-protein coupled receptors through which the HIV virus enters and infects cells. Both receptors are also related to HIV-associated neurocognitive disorders that include difficulties in concentration and memory, impaired executive functions, psychomotor slowing, depression and irritability, which are also hallmarks of the long-term sequelae of TBI. Moreover, A growing body of evidence attributes negative influences to CCR5 activation on cognition, particularly after stroke and traumatic brain injury (TBI). Here we investigated the effect of their blockage on motor and cognitive functions, on brain tissue loss and preservation and on some of the biochemical pathways involved. We examined the effect of maraviroc, a CCR5 antagonist used in HIV patients as a viral entry inhibitor, and of plerixafor (AMD3100), a CXCR4 antagonist used in cancer patients as an immune-modulator, on mice subjected to closed head injury (CHI). Mice were treated with maraviroc or plerixafor after CHI for the following 4 or 5 days, respectively. Neurobehavior was assessed according to the Neurological Severity Score; cognitive tests were performed by using the Y-maze, Barnes maze and the novel object recognition test; anxiety was evaluated with the open field test. The mice were sacrificed and brain tissues were collected for Western blot, pathological and immunohistochemical analyses. Both drugs enhanced tissue preservation in the cortex, hippocampus, periventricular areas, corpus callosum and striatum, and reduced astrogliosis)GFAP expression). They also increased the levels of synaptic cognition-related signaling molecules such as phosphorylated NR1 and CREB, and the synaptic plasticity protein PSD95. Both treatments also enhanced the expression of CCR5 and CXCR4 on different brain cell types. In summary, the beneficial effects of blocking CCR5 and CXCR4 after CHI suggest that the drugs used in this study, both FDA approved and in clinical use, should be considered for translational research in TBI patients.

Potential roles of stem cell marker genes in axon regeneration

Axon regeneration is orchestrated by many genes that are differentially expressed in response to injury. Through a comparative analysis of gene expression profiling, injury-responsive genes that are potential targets for understanding the mechanisms underlying regeneration have been revealed. As the efficiency of axon regeneration in both the peripheral and central nervous systems can be manipulated, we suggest that identifying regeneration-associated genes is a promising approach for developing therapeutic applications in vivo. Here, we review the possible roles of stem cell marker- or stemness-related genes in axon regeneration to gain a better understanding of the regeneration mechanism and to identify targets that can enhance regenerative capacity.

Rare homozygous nonsense variant in AIMP1 causing Early Onset Epileptic Encephalopathy with Burst Suppression (EOEE-BS)

Pathogenic variants in AIMP1 gene are rare causes of neurologic disorders. Homozygous frameshift and nonsense variants in AIMP1 have been described in severe neurodegenerative disease. This is the third report of a homozygous nonsense variant in AIMP1 [c.115 C > T (p.Gln39*)] in a girl with severe neonatal onset epileptic encephalopathy. Like the two other cases reported, our patient is also of Filipino descent. Clinical features include microcephaly, poor visual motor development, shallow breathing, severe hypertonia in extremities, severe global developmental delay, poor gag and suck reflex, failure to thrive in the neonatal period, and early onset intractable seizures. Brain MRI showed hypoplasia of corpus callosum as well as cerebellar vermis, global volume loss and diminished myelination for her age. Electroencephalogram at four months of age showed background consisting of synchronous and asynchronous intervals of burst suppression with intermittent multifocal spikes predominantly in the bi-temporal region, suggestive of Early Onset Epileptic Encephalopathy with Burst Suppression (EOEE-BS) which has not been previously associated with the c.115 C > T variant in AIMP1. Of note, she presented to us in super refractory status epilepticus which was eventually controlled after administration of ketogenic diet and Epidiolex (cannabidiol). This report expands the genetic landscape of EOEE-BS. This is the first case of this specific variant in which Epidiolex was administered, which along with Ketogenic diet aided in controlling patient's super refractory status epilepticus.

Serum neurofilament light chain (NFL) remains unchanged during electroconvulsive therapy

Objectives: Although there is consistent evidence that electroconvulsive therapy (ECT) is safe and well tolerated by the majority of patients, some authors still accuse ECT to inevitably cause brain damage and permanent memory loss, assertions that may increase patients' worries about a useful treatment. Recently, the measurement of neurofilament light chain (NFL) in peripheral blood was technically implemented, permitting longitudinal analysis of this biomarker for axonal damage. NFL is part of the axonal cytoskeleton and is released into the CSF and peripheral blood in the context of neuronal damage.Methods: In our study, blood from 15 patients with major depressive disorder receiving ECT was collected before the first ECT as well as 24 h and seven days after the last ECT, respectively. NFL concentrations were analysed using the ultrasensitive single molecule array (Simoa) technology.Results: NFL concentrations did not differ between patients and healthy controls, and there was no significant change in NFL levels in the course of ECT. On the contrary, we even found a slight decrease in absolute NFL concentrations.Conclusions: Our study confirms the safety of ECT by using a most sensitive method for the detection of NFL in peripheral blood as a biomarker of neuronal damage.

Altered Features of Vimentin-containing Cells in Cerebrum of Tg(SOD1*G93A)1Gur Mice: A Preliminary Study on Cerebrum Endogenous Neural Precursor Cells in Amyotrophic Lateral Sclerosis

Vimentin-containing cells (VCCs) are potential neural precursor cells in central nervous systems, Thus, we studied the alteration of VCCs proliferation, differentiation and migration in the cerebrum during different stages of Tg(SOD1*G93A)1Gur mice. It aims to search potential ways regulating the proliferation, differentiation and migration of endogenous VCCs, to enhance their neural repair function and to cure or prevent from the development of ALS. We observed and analyzed the proliferation, differentiation and migration of VCCs in different anatomic regions and cell types of cerebrum at different stages including the pre-onset (60-70 days), onset (90-100 days) and progression (120-130 days) of wild-type (WT) and Tg(SOD1*G93A)1Gur mice using the fluorescent immunohistochemical technology. Results showed that VCCs in the cerebrum were mostly distributed in the ventricular system, periventricular structures, the hippocampus and the cerebral cortex in WT mice. VCCs significantly reduced in the motor cortex and the cingulate cortex in Tg(SOD1*G93A)1Gur mice. All vimentin expressed in the extranuclear and almost all VCCs were astrocytes in WT mice and Tg(SOD1*G93A)1Gur mice. There were no significant difference in the number of Brdu and nestin positive cells in left and right brains of WT mice and Tg(SOD1*G93A)1Gur mice in the period of 60-130 days. Our data suggested that there existed extensively NPCs in the cerebrum of adult mice. In ALS-like Tg(SOD1*G93A)1Gur mice, VCCs in the motor cortex, the olfactory cortex and the cingulate cortex showed that no any proliferation and redistribution in neural cells of VCCs in the cerebrum occurred in all stages of ALS, might migrate to damaged regions.

Colonic mast cell numbers, symptom profile, and mucosal expression of elements of the epithelial barrier in irritable bowel syndrome

BACKGROUND

This study aimed to determine whether patients with IBS displayed altered mucosal mast cell (MC) numbers and proportions of MCs co-localizing with nerves compared with healthy subjects (HS) and whether these MC characteristics correlated with IBS symptoms, elements of the epithelial barrier, or visceral sensitivity.

METHODS

Mucosal MC characteristics were determined using immunoassay. IBS symptoms, gene expression of elements of the epithelial barrier, fecal serine protease activity, and visceral sensitivity were assessed.

KEY RESULTS

The MC numbers per mm² were 2.0 (0.0-6.0) in patients with IBS (n = 43) and 3.5 (1.1-9.1) in HS (n = 20, P = .26). Of these, MCs were 0.0 (0.0-20) % vs 3.1 (0.0-18) % (P = .76) in IBS and HS, respectively, in co-localization with nerve fibers. MC characteristics were equivalent in the different IBS subtypes. Hierarchical cluster analysis identified two distinct groups among patients with IBS: MC high (higher MC numbers and proportions of MCs co-localizing with nerves) and MC low (lower MC numbers and proportions of MCs co-localizing with nerves). The MC high and MC low groups could not be discriminated with regard to IBS symptoms, parameters of visceral sensitivity, gene expression of elements of the epithelial barrier, and fecal protease activity.

CONCLUSION AND INFERENCES

There was no evidence of increased infiltration or altered localization of MCs in the colonic mucosa of patients with IBS. These MC characteristics were not linked to global IBS symptoms or mucosal expression of elements of the epithelial barrier. These findings indicate that quantity and location of mucosal MCs are factors not involved in the pathophysiology of IBS.

iTRAQ-based proteomic analysis discovers potential biomarkers of diffuse axonal injury in rats

Diffuse axonal injury (DAI) is one of the most common and severe pathological consequences of traumatic brain injury (TBI). The molecular mechanism of DAI is highly complicated and still elusive, yet a clear understanding is crucial for the diagnosis, treatment, and prognosis of DAI. In our study, we used rats to establish a DAI model and applied isobaric tags for relative and absolute quantitation (iTRAQ) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to identify differentially expressed proteins (DEPs) in the corpus callosum. As a result, a total of 514 proteins showed differential expression between the injury groups and the control. Among these DEPs, 14 common DEPs were present at all seven time points postinjury (1, 3, 6, 12, 24, 48, and 72 h). Next, bioinformatic analysis was performed to elucidate the pathogenesis of DAI, which was found to possibly involve calcium ion-regulatory proteins (e.g., calsenilin and ryanodine receptor 2), cytoskeleton organization (e.g., peripherin, NFL, NFM, and NFH), apoptotic processes (e.g., calsenilin and protein kinase C delta type), and inflammatory response proteins (e.g., complement C3 and C-reactive protein). Moreover, peripherin and calsenilin were successfully confirmed by western blotting to be significantly upregulated during DAI, and immunohistochemical (IHC) analysis revealed that their expression increased and could be observed in axons after injury, thus indicating their potential as DAI biomarkers. Our experiments not only provide insight into the molecular mechanisms of axonal injury in rats during DAI but also give clinicians and pathologists important reference data for the diagnosis of DAI. Our findings may expand the list of DAI biomarkers and improve the postmortem diagnostic rate of DAI.

Serum Neurofilament Light Chain Concentration Correlates with Infarct Volume but Not Prognosis in Acute Ischemic Stroke

BACKGROUND AND PURPOSE

We studied serum neurofilaments diagnostic value in patients with acute ischemic stroke (AIS) or TIA and evaluated any correlation with symptom severity, cerebral infarction volume, aetiology, and clinical outcome.

METHODS

One hundred and thirty-six patients (101 with AIS, and 35 with TIA) were included. Acute-phase serum neurofilament light chain (sNfL) was analyzed with a novel ultrasensitive single molecule array (Simoa). Cerebral infarction volume was measured from brain computed tomography in the subacute phase (>2 days). Stroke aetiology was defined by trial of ORG 10172 in acute stroke treatment classification, severity by National Institute of Health stroke scale (NIHSS) and the degree of disability by the Modified Rankin Scale (mRS) after 90 days.

RESULTS

sNfL was markedly higher in patients with AIS (89.5 pg/mL [IQR: 44.7-195.3]) than with TIA (25.2 pg/mL [IQR: 14.6-48.0]), P= <.001), also after adjusting for age, NIHSS, and stroke volume (P= .003). In receiver operating characteristic analysis, sNfL concentration greater than or equal to 49 pg/mL proved to be the best cut-off value to differentiate between patients with stroke and those with TIA (sensitivity of 73% and specificity of 80%). sNfL concentration significantly correlated with cerebral infarction volume (r = .413, P= <.001), this association remained significant after adjusting for established predictors (P= .019). Patients with AIS due to cardioembolism or large artery atherosclerosis had the highest sNfL concentrations. NIHSS on admission (r = .343, P = <.001) and mRS scores after 3 months (r = .306, P = .004) correlated with sNfL concentration, however functional outcome 3 months after stroke was not associated with sNfL after adjusting for potential confounders.

CONCLUSIONS

Cases with stroke were distinguishable from those with TIA following the determination of sNfL in the blood samples. The presence and amount of axonal damage estimated by sNfL correlated with the final cerebral infarction volume but was not predictive of degree of disability.

Chemotherapy-Induced Peripheral Neuropathy and Changes in Cytoskeleton

Despite the different antineoplastic mechanisms of action, peripheral neurotoxicity induced by all chemotherapy drugs (anti-tubulin agents, platinum compounds, proteasome inhibitors, thalidomide) is associated with neuron morphological changes ascribable to cytoskeleton modifications. The “dying back” degeneration of distal terminals (sensory nerves) of dorsal root ganglia sensory neurons, observed in animal models, in in vitro cultures and biopsies of patients is the most evident hallmark of the perturbation of the cytoskeleton. On the other hand, in highly polarized cells like neurons, the cytoskeleton carries out its role not only in axons but also has a fundamental role in dendrite plasticity and in the organization of soma. In the literature, there are many studies focused on the antineoplastic-induced alteration of microtubule organization (and consequently, fast axonal transport defects) while very few studies have investigated the effect of the different classes of drugs on microfilaments, intermediate filaments and associated proteins. Therefore, in this review, we will focus on: (1) Highlighting the fundamental role of the crosstalk among the three filamentous subsystems and (2) investigating pivotal cytoskeleton-associated proteins.

Pathogenic variants in AIMP1 cause pontocerebellar hypoplasia

Aminoacyl-tRNA synthetase-interacting multifunctional protein 1 (AIMP1) is a non-catalytic component of the multi-tRNA synthetase complex which catalyzes the ligation of amino acids to the correct tRNAs. Pathogenic variants in several aminoacyl-tRNA synthetases genes have been linked to various neurological disorders, including leukodystrophies and pontocerebellar hypoplasias (PCH). To date, loss-of-function variants in AIMP1 have been associated with hypomyelinating leukodystrophy-3 (MIM 260600). Here, we report a novel frameshift AIMP1 homozygous variant (c.160delA,p.Lys54Asnfs) in a child with pontocerebellar hypoplasia and simplified gyral pattern, a phenotype not been previously described with AIMP1 variants, thus expanding the phenotypic spectrum. AIMP1 should be included in diagnostic PCH gene panels.

Biallelic Loss-of-Function Variants in AIMP1 Cause a Rare Neurodegenerative Disease

AIMP1/p43, is a noncatalytic component of the mammalian multi-tRNA synthetase complex that catalyzes the ligation of amino acids to their cognate tRNAs. AIMP1 is largely expressed in the central nervous system, where it is part of the regulatory machine of the neurofilament assembly, playing a crucial role in neuronal development and function. To date, nonsense mutations in AIMP1 have been associated with a primary neurodegenerative disorder consisting of cerebral atrophy, hypomyelination, microcephaly and epilepsy, whereas missense mutations have recently been linked to intellectual disability without neurodegeneration. Here, we report the first French-Canadian patient with a novel frameshift AIMP1 homozygous mutation (c.191_192delAA, p.Gln64Argfs*25), resulting in a severe neurodegenerative phenotype. We review and discuss the phenotypic spectrum associated with AIMP1 pathogenic variants.

Hypothermic treatment after computer-controlled compression in minipig: A preliminary report on the effect of epidural vs. direct spinal cord cooling

The aim of the present study was to investigate the therapeutic efficacy of local hypothermia (beginning 30 min post-injury persisting for 5 h) on tissue preservation along the rostro-caudal axis of the spinal cord (3 cm cranially and caudally from the lesion site), and the prevention of injury-induced functional loss in a newly developed computer-controlled compression model in minipig (force of impact 18N at L3 level), which mimics severe spinal cord injury (SCI). Minipigs underwent SCI with two post-injury modifications (durotomy vs. intact dura mater) followed by hypothermia through a perfusion chamber with cold (epidural t≈15°C) saline, DMEM/F12 or enriched DMEM/F12 (SCI/durotomy group) and with room temperature (t≈24°C) saline (SCI-only group). Minipigs treated with post-SCI durotomy demonstrated slower development of spontaneous neurological improvement at the early postinjury time points, although the outcome at 9 weeks of survival did not differ significantly between the two SCI groups. Hypothermia with saline (t≈15°C) applied after SCI-durotomy improved white matter integrity in the dorsal and lateral columns in almost all rostro-caudal segments, whereas treatment with medium/enriched medium affected white matter integrity only in the rostral segments. Furthermore, regeneration of neurofilaments in the spinal cord after SCI-durotomy and hypothermic treatments indicated an important role of local saline hypothermia in the functional outcome. Although saline hypothermia (24°C) in the SCI-only group exhibited a profound histological outcome (regarding the gray and white matter integrity and the number of motoneurons) and neurofilament protection in general, none of the tested treatments resulted in significant improvement of neurological status. The findings suggest that clinically-proven medical treatments for SCI combined with early 5 h-long saline hypothermia treatment without opening the dural sac could be more beneficial for tissue preservation and neurological outcome compared with hypothermia applied after durotomy.

A Single Dose of Atorvastatin Applied Acutely after Spinal Cord Injury Suppresses Inflammation, Apoptosis, and Promotes Axon Outgrowth, Which Might Be Essential for Favorable Functional Outcome

The aim of our study was to limit the inflammatory response after a spinal cord injury (SCI) using Atorvastatin (ATR), a potent inhibitor of cholesterol biosynthesis. Adult Wistar rats were divided into five experimental groups: one control group, two Th9 compression (40 g/15 min) groups, and two Th9 compression + ATR (5 mg/kg, i.p.) groups. The animals survived one day and six weeks. ATR applied in a single dose immediately post-SCI strongly reduced IL-1β release at 4 and 24 h and considerably reduced the activation of resident cells at one day post-injury. Acute ATR treatment effectively prevented the excessive infiltration of destructive M1 macrophages cranially, at the lesion site, and caudally (by 66%, 62%, and 52%, respectively) one day post-injury, whereas the infiltration of beneficial M2 macrophages was less affected (by 27%, 41%, and 16%). In addition, at the same time point, ATR visibly decreased caspase-3 cleavage in neurons, astrocytes, and oligodendrocytes. Six weeks post-SCI, ATR increased the expression of neurofilaments in the dorsolateral columns and Gap43-positive fibers in the lateral columns around the epicenter, and from day 30 to 42, significantly improved the motor activity of the hindlimbs. We suggest that early modulation of the inflammatory response via effects on the M1/M2 macrophages and the inhibition of caspase-3 expression could be crucial for the functional outcome.

Molecular Determinants of Malignant Brain Cancers: From Intracellular Alterations to Invasion Mediated by Extracellular Vesicles

Malignant glioma cells invade the surrounding brain parenchyma, by migrating along the blood vessels, thus promoting cancer growth. The biological bases of these activities are grounded in profound alterations of the metabolism and the structural organization of the cells, which consequently acquire the ability to modify the surrounding microenvironment, by altering the extracellular matrix and affecting the properties of the other cells present in the brain, such as normal glial-, endothelial- and immune-cells. Most of the effects on the surrounding environment are probably exerted through the release of a variety of extracellular vesicles (EVs), which contain many different classes of molecules, from genetic material to defined species of lipids and enzymes. EV-associated molecules can be either released into the extracellular matrix (ECM) and/or transferred to neighboring cells: as a consequence, both deep modifications of the recipient cell phenotype and digestion of ECM components are obtained, thus causing cancer propagation, as well as a general brain dysfunction. In this review, we first analyze the main intracellular and extracellular transformations required for glioma cell invasion into the brain parenchyma; then we discuss how these events may be attributed, at least in part, to EVs that, like the pawns of a dramatic chess game with cancer, open the way to the tumor cells themselves.

Type III Intermediate Filaments Desmin, Glial Fibrillary Acidic Protein (GFAP), Vimentin, and Peripherin

SummaryType III intermediate filament (IF) proteins assemble into cytoplasmic homopolymeric and heteropolymeric filaments with other type III and some type IV IFs. These highly dynamic structures form an integral component of the cytoskeleton of muscle, brain, and mesenchymal cells. Here, we review the current ideas on the role of type III IFs in health and disease. It turns out that they not only offer resilience to mechanical strains, but, most importantly, they facilitate very efficiently the integration of cell structure and function, thus providing the necessary scaffolds for optimal cellular responses upon biochemical stresses and protecting against cell death, disease, and aging.

Modeling phenotypes of malignant gliomas

Malignant gliomas are primary tumors of the central nervous system characterized by diffuse infiltration into the brain and a high recurrence rate. Advances in comprehensive genomic studies have provided unprecedented insight into the genetic and molecular heterogeneity of these tumors and refined our understanding of their evolution from low to high grade. However, similar levels of phenotypic characterization are indispensable to understanding the complexity of malignant gliomas. Experimental glioma models have also achieved great progress in recent years. Advances in transgenic technologies and cell culture have allowed the establishment of mouse models that mirror the human disease with increasing fidelity and which support single-cell resolution for phenotypic analyses. Here we review the major types of preclinical glioma models, with an emphasis on how recent developments in experimental modeling have shed new light on two fundamental aspects of glioma phenotype, their cell of origin and their invasive potential.

Transient vimentin expression during the embryonic development of the chicken cerebellum

Complex morphogenetic events, critical for the development of normal cerebellum foliation and layering, are known to involve type III intermediate filament protein such as vimentin expressed by Bergmann glia. The present study aimed to determine aspects of intermediate and late embryonic pattern of vimentin expression during the corticogenesis of chicken cerebellum at embryonic days 10-19 (E10-E19), using single and double immunohistochemistry/immunofluorescence. Vimentin expression showed partial co-localization with the glial markers GFAP and BLBP. Within cerebellar cortex, vimentin+ fibers were first found within lobules I and X (E10) and gradually extended to all folia (E15-E17), located within the external granule (EGL) the molecular cell layer, showing a radial orientation towards the inner granular layer and the cerebellar white matter oriented longitudinally. Interestingly, within the immature fissures base of most lobules, vimentin+ fibers radiate in a fan shape. Short-term BrdU experiments revealed that EGL cell proliferation was higher in the fissure base compared to folia apex. In addition, following 24-h survival, BrdU+ cells were found in close association to vimentin+ fibers in the EGL pre-migratory zone and within immature molecular layer. Paralleling cerebellum development, vimentin expression gradually extended to all folia sub-regions (base, wall, apex), but, at day E19, it was mainly confined to the folia apex and secondary fissure base. Taken together our data further support the possible role of vimentin+ fibers in the structural events of cerebellum corticogenesis, suggesting the participation of radial/Bergmann glia in chicken cerebellum foliation, similarly to that described for mammalian cerebellum morphogenesis.

BPAG1 in muscles: Structure and function in skeletal, cardiac and smooth muscle

BPAG1, also known as Dystonin or BP230, belongs to the plakin family of proteins, which has multiple cytoskeleton-binding domains. Several BPAG1 isoforms are produced by a single BPAG1 genomic locus using different promoters and exons. For example, BPAG1a, BPAG1b, and BPAG1e are predominantly expressed in the nervous system, muscle, and skin, respectively. Among BPAG1 isoforms, BPAG1e is well studied because it was first identified as an autoantigen in patients with bullous pemphigoid, an autoimmune skin disease. BPAG1e is a component of hemidesmosomes, the adhesion complexes that promote dermal-epidermal cohesion. In the nervous system, the role of BPAG1a is also well studied because disruption of BPAG1a results in a phenotype identical to that of Dystonia musculorum (dt) mutants, which show progressive motor disorder. However, the expression and function of BPAG1 in muscles is not well studied. The aim of this review is to provide an overview of and highlight some recent findings on the expression and function of BPAG1 in muscles, which can assist future studies designed to delineate the role and regulation of BPAG1 in the dt mouse phenotype and in human hereditary sensory and autonomic neuropathy type 6 (HSAN6).

Association between cerebrospinal fluid and plasma neurodegeneration biomarkers with brain atrophy in Alzheimer's disease

The aggregation and deposition of amyloid-β (Aβ) peptides into plaques is an early event in Alzheimer's disease (AD), which is followed by different aspects of neurodegeneration that can be measured in the cerebrospinal fluid (CSF) or plasma using neurofilament light (NFL), neurogranin (Ng), total Tau (T-Tau), and phosphorylated tau (P-Tau) levels. The relationship between these biomarkers and regional brain atrophy across the different stages of AD remains largely unexplored. In this study, we assessed whether NFL, Ng, T-Tau, and P-Tau levels in CSF and NFL in plasma are associated with cortical thinning and subcortical volume loss in cognitively normal, mild cognitive impairment, and AD subjects with and without Aβ pathology. Our main findings showed that CSF NFL levels were associated with brain atrophy in all groups, but plasma NFL only correlated with atrophy in symptomatic cases. In contrast, Ng was associated with regional brain atrophy only in individuals with Aβ pathology. Altogether, our main findings suggest that Ng is strongly associated with Aβ pathology, whereas NFL is more unspecific.

TDP-43 and Cytoskeletal Proteins in ALS

Amyotrophic lateral sclerosis (ALS) represents a rapidly progressing neurodegenerative disease and is characterized by a degeneration of motor neurons. Motor neurons are particularly susceptible to selective and early degeneration because of their extended axon length and their dependency on the cytoskeleton for its stability, signaling, and axonal transport. The motor neuron cytoskeleton comprises actin filaments, neurofilaments like peripherin, and microtubules. The Transactivating Response Region (TAR) DNA Binding Protein (TDP-43) forms characteristic cytoplasmic aggregates in motor neurons of ALS patients, and at least in part, the pathogenesis of ALS seems to be driven by toxic pTDP-43 aggregates in cytoplasm, which lead to a diminished axon formation and reduced axon length. Diminished axon formation and reduced axon length suggest an interaction of TDP-43 with the cytoskeleton of motor neurons. TDP-43 interacts with several cytoskeletal components, e.g., the microtubule-associated protein 1B (MAP1B) or the neurofilament light chain (NFL) through direct binding to its RNA. From a clinical perspective, cytoskeletal biomarkers like phosphorylated neurofilament heavy chain (pNFH) and NFL are already clinically used in ALS patients to predict survival, disease progression, and duration. Thus, in this review, we focus on the interaction of TDP-43 with the different cytoskeleton components such as actin filaments, neurofilaments, and microtubules as well as their associated proteins as one aspect in the complex pathogenesis of ALS.

Neurons of the rat cervical spinal cord express vimentin and neurofilament after intraparenchymal injection of kainic acid

Intermediate filaments (IF) can be altered under disorders such as neurodegenerative diseases. Kainic acid (KA) induce behavioral changes and histopathological alterations of the spinal cord of injected rats. Our goal was to evaluate the IF expression in neurons during this injury model. Animals were injected with KA at the C5 segment of the cervical spinal cord and euthanized at 1, 3 and 7 post injection (pi) days. Neuronal cell counting showed a significant loss of neurons at the injection site when compared with those of sham and non-operated animals. Immunohistochemistry for vimentin and neurofilament showed positive labeling of perikarya in sham and KA-injected animals since day 1 pi that lasted for the remaining experimental days. Colocalization analysis between enolase and vimentin or neurofilament confirmed a high index of colocalization in both experimental groups at day 1 pi. This index decreased in sham animals by day 3 pi whereas that of KA-injected animals remained high throughout the experiment. These results may suggest that perikarya initiate an unconventional IF expression, which may respond to the neuronal damage induced by the mechanical injury and the excitotoxic effect of KA. It seems that vimentin and neurofilament expression may be a necessary change to promote recovery of the damaged tissue.

Serum neurofilament light protein predicts clinical outcome in traumatic brain injury

Axonal white matter injury is believed to be a major determinant of adverse outcomes following traumatic brain injury (TBI). We hypothesized that measurement of neurofilament light protein (NF-L), a protein found in long white-matter axons, in blood samples, may serve as a suitable biomarker for neuronal damage in TBI patients. To test our hypotheses, we designed a study in two parts: i) we developed an immunoassay based on Single molecule array technology for quantification of NF-L in blood, and ii) in a proof-of-concept study, we tested our newly developed method on serial serum samples from severe TBI (sTBI) patients (n = 72) and controls (n = 35). We also compared the diagnostic and prognostic utility of NF-L with the established blood biomarker S100B. NF-L levels were markedly increased in sTBI patients compared with controls. NF-L at admission yielded an AUC of 0.99 to detect TBI versus controls (AUC 0.96 for S100B), and increased to 1.00 at day 12 (0.65 for S100B). Importantly, initial NF-L levels predicted poor 12-month clinical outcome. In contrast, S100B was not related to outcome. Taken together, our data suggests that measurement of serum NF-L may be useful to assess the severity of neuronal injury following sTBI.

Early Cytoskeletal Protein Modifications Precede Overt Structural Degeneration in the DBA/2J Mouse Model of Glaucoma

Axonal transport deficits precede structural loss in glaucoma and other neurodegenerations. Impairments in structural support, including modified cytoskeletal proteins, and microtubule-destabilizing elements, could be initiating factors in glaucoma pathogenesis. We investigated the time course of changes in protein levels and post-translational modifications in the DBA/2J mouse model of glaucoma. Using anterograde tract tracing of the retinal projection, we assessed major cytoskeletal and transported elements as a function of transport integrity in different stages of pathological progression. Using capillary-based electrophoresis, single- and multiplex immunosorbent assays, and immunofluorescence, we quantified hyperphosphorylated neurofilament-heavy chain, phosphorylated tau (ptau), calpain-mediated spectrin breakdown product (145/150 kDa), β–tubulin, and amyloid-β₄₂ proteins based on age and transport outcome to the superior colliculus (SC; the main retinal target in mice). Phosphorylated neurofilament-heavy chain (pNF-H) was elevated within the optic nerve (ON) and SC of 8–10 month-old DBA/2J mice, but was not evident in the retina until 12–15 months, suggesting that cytoskeletal modifications first appear in the distal retinal projection. As expected, higher pNF-H levels in the SC and retina were correlated with axonal transport deficits. Elevations in hyperphosphorylated tau (ptau) occurred in ON and SC between 3 and 8 month of age while retinal ptau accumulations occurred at 12–15 months in DBA/2J mice. In vitro co-immunoprecipitation experiments suggested increased affinity of ptau for the retrograde motor complex protein dynactin. We observed a transport-related decrease of β-tubulin in ON of 10–12 month-old DBA/2J mice, suggesting destabilized microtubule array. Elevations in calpain-mediated spectrin breakdown product were seen in ON and SC at the earliest age examined, well before axonal transport loss is evident. Finally, transport-independent elevations of amyloid-β₄₂, unlike pNF-H or ptau, occurred first in the retina of DBA/2J mice, and then progressed to SC. These data demonstrate distal-to-proximal progression of cytoskeletal modifications in the progression of glaucoma, with many of these changes occurring prior to complete loss of functional transport and axon degeneration. The earliest changes, such as elevated spectrin breakdown and amyloid-β levels, may make retinal ganglion cells susceptible to future stressors. As such, targeting modification of the axonal cytoskeleton in glaucoma may provide unique opportunities to slow disease progression.

Neurofilament depletion improves microtubule dynamics via modulation of Stat3/stathmin signaling

In neurons, microtubules form a dense array within axons, and the stability and function of this microtubule network is modulated by neurofilaments. Accumulation of neurofilaments has been observed in several forms of neurodegenerative diseases, but the mechanisms how elevated neurofilament levels destabilize axons are unknown so far. Here, we show that increased neurofilament expression in motor nerves of pmn mutant mice, a model of motoneuron disease, causes disturbed microtubule dynamics. The disease is caused by a point mutation in the tubulin-specific chaperone E (Tbce) gene, leading to an exchange of the most C-terminal amino acid tryptophan to glycine. As a consequence, the TBCE protein becomes instable which then results in destabilization of axonal microtubules and defects in axonal transport, in particular in motoneurons. Depletion of neurofilament increases the number and regrowth of microtubules in pmn mutant motoneurons and restores axon elongation. This effect is mediated by interaction of neurofilament with the stathmin complex. Accumulating neurofilaments associate with stathmin in axons of pmn mutant motoneurons. Depletion of neurofilament by Nefl knockout increases Stat3–stathmin interaction and stabilizes the microtubules in pmn mutant motoneurons. Consequently, counteracting enhanced neurofilament expression improves axonal maintenance and prolongs survival of pmn mutant mice. We propose that this mechanism could also be relevant for other neurodegenerative diseases in which neurofilament accumulation and loss of microtubules are prominent features.

Dynamic self-guiding analysis of Alzheimer's disease

We applied a self-guiding evolutionary algorithm to initiate the synthesis of the Alzheimer's disease-related data and literature. A protein interaction network associated with amyloid-beta precursor protein (APP) and a seed model that treats Alzheimer's disease as progressive dysregulation of APP-associated signaling were used as dynamic “guides” and structural “filters” in the recursive search, analysis, and assimilation of data to drive the evolution of the seed model in size, detail, and complexity. Analysis of data and literature across sub-disciplines and system-scale discovery platforms suggests a key role of dynamic cytoskeletal connectivity in the stability, plasticity, and performance of multicellular networks and architectures. Chronic impairment and/or dysregulation of cell adhesions/synapses, cytoskeletal networks, and/or reversible epithelial-to-mesenchymal-like transitions, which enable and mediate the stable and coherent yet dynamic and reconfigurable multicellular architectures, may lead to the emergence and persistence of the disordered, wound-like pockets/microenvironments of chronically disconnected cells. Such wound-like microenvironments support and are supported by pro-inflammatory, pro-secretion, de-differentiated cellular phenotypes with altered metabolism and signaling. The co-evolution of wound-like microenvironments and their inhabitants may lead to the selection and stabilization of degenerated cellular phenotypes, via acquisition of epigenetic modifications and mutations, which eventually result in degenerative disorders such as cancer and Alzheimer's disease.

Disrupted axon-glia interactions at the paranode in myelinated nerves cause axonal degeneration and neuronal cell death in the aged Caspr mutant mouse shambling

Emerging evidence suggests that axonal degeneration is a disease mechanism in various neurodegenerative diseases and that the paranodes at the nodes of Ranvier may be the initial site of pathogenesis. We investigated the pathophysiology of the disease process in the central and peripheral nervous systems of a Caspr mutant mouse, shambling (shm), which is affected by disrupted paranodal structures and impaired nerve conduction of myelinated nerves. The shm mice manifest a progressive neurological phenotype as mice age. We found extensive axonal degeneration and a loss of neurons in the central nervous system and peripheral nervous system in aged shm mice. Axonal alteration of myelinated nerves was defined by abnormal distribution and expression of neurofilaments and derangements in the status of phosphorylated and non/de-phosphorylated neurofilaments. Autophagy-related structures were also accumulated in degenerated axons and neurons. In conclusion, our results suggest that disrupted axon-glia interactions at the paranode cause the cytoskeletal alteration in myelinated axons leading to neuronal cell death, and the process involves detrimental autophagy and aging as factors that promote the pathogenesis.

Composite bottlebrush mechanics: α-internexin fine-tunes neurofilament network properties

Neuronal cytoplasmic intermediate filaments are principal structural and mechanical elements of the axon. Their expression during embryonic development follows a differential pattern, while their unregulated expression is correlated to neurodegenerative diseases. The largest neurofilament proteins of medium (NF-M) and high molecular weight (NF-H) were shown to modulate the axonal architecture and inter-filament spacing. However, the individual roles of the remaining α-internexin (α-Inx) and neurofilament of low molecular weight (NF-L) proteins in composite filaments remained elusive. In contrast to previous predictions, we show that when co-assembled with NF-M, the shortest and the least charged α-Inx protein increases inter-filament spacing. These findings suggest a novel structural explanation for the expression pattern of neurofilament proteins during embryonic development. We explain our results by an analysis of ionic cross-links between the disordered polyampholytic C-terminal tails and suggest that a collapsed conformation of the α-Inx tail domain interferes with tail cross-linking near the filament backbone.

Missense variants in AIMP1 gene are implicated in autosomal recessive intellectual disability without neurodegeneration

AIMP1/p43 is a multifunctional non-catalytic component of the multisynthetase complex. The complex consists of nine catalytic and three non-catalytic proteins, which catalyze the ligation of amino acids to their cognate tRNA isoacceptors for use in protein translation. To date, two allelic variants in the AIMP1 gene have been reported as the underlying cause of autosomal recessive primary neurodegenerative disorder. Here, we present two consanguineous families from Pakistan and Iran, presenting with moderate to severe intellectual disability, global developmental delay, and speech impairment without neurodegeneration. By the combination of homozygosity mapping and next generation sequencing, we identified two homozygous missense variants, p.(Gly299Arg) and p.(Val176Gly), in the gene AIMP1 that co-segregated with the phenotype in the respective families. Molecular modeling of the variants revealed deleterious effects on the protein structure that are predicted to result in reduced AIMP1 function. Our findings indicate that the clinical spectrum for AIMP1 defects is broader than witnessed so far.